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91.
B P Yu D W Lee C G Marler J H Choi 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1990,193(1):13-15
The major difficulty in defining the mechanisms for the action of food restriction relates to its diversity and lack of specificity. In searching for the common factor(s) and commonality involved in such diversified effects, a cellular homeostasis mechanism is proposed. A study initiated in our laboratory strongly indicates that the cellular homeostatic mechanism is seriously compromised by oxidative damage of free radical reaction with aging. Data on mitochondrial hydroperoxide, microsomal cytochrome P-450 breakdown, and reduction of cytosolic antioxidant capacity support the notion. Remarkably, food restriction attenuates all of these age-related changes. It is concluded therefore that food restriction preserves the homeostatic regulatory processes by maintaining the integrity of (i) membrane structure and function, (ii) proper redox state of cellular components, and (iii) detoxification process of xenobiotics. 相似文献
92.
Molecular analyses of the lactococcin A gene cluster from Lactococcus lactis subsp. lactis biovar diacetylactis WM4. 总被引:12,自引:10,他引:2
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The genes responsible for bacteriocin production and immunity in Lactococcus lactis subsp. lactis biovar diacetylactis WM4 were localized and characterized by DNA restriction fragment deletion, subcloning, and nucleotide sequence analysis. The nucleotide sequence of a 5.6-kb AvaII restriction fragment revealed a cluster with five complete open reading frames (ORFs) in the same orientation. DNA and protein homology analyses, combined with deletion and Tn5 insertion mutagenesis, implicated four of the ORFs in the production of and immunity to lactococcin A. The last two ORFs in the cluster were the lactococcin A structural and immunity genes, lcnA and lciA. The two ORFs immediately upstream of lcnA and lciA were designated lcnC and lcnD, and the proteins that they encoded showed similarities to proteins of signal sequence-independent secretion systems. lcnC encodes a protein of 716 amino acids that could belong to the HlyB family of ATP-dependent membrane translocators. LcnC contains an ATP binding domain in a conserved C-terminal stretch of approximately 200 amino acids and three putative hydrophobic segments in the N terminus. The lcnD product, LcnD, of 474 amino acids, is essential for lactococcin A expression and shows structural similarities to HlyD and its homologs. On the basis of these results, a secretion apparatus that is essential for the full expression of active lactococcin A is postulated. 相似文献
93.
K H Kong M Nishida H Inoue K Takahashi 《Biochemical and biophysical research communications》1992,182(3):1122-1129
The glutathione (GSH)-conjugating activity of human class Pi glutathione S-transferase (GST pi) toward 1-chloro-2,4-dinitrobenzene (CDNB) was significantly lowered by reaction with N-acetylimidazole, an O-acetylating reagent for tyrosine residues. Further, the replacement of Tyr7 in GST pi, which is conserved in all cytosolic GSTs, with phenylalanine by site-directed mutagenesis also lowered the activities toward CDNB and ethacrynic acid. The Km values of the mutant for both GSH and CDNB were almost equivalent to those of the wild type, while the Vmax of the former was about 55-fold smaller than that of the latter. Therefore, Tyr7 is considered to be an essential residue for the catalytic activity of GST pi. 相似文献
94.
TGF-beta and retinoic acid: regulators of growth and modifiers of differentiation in human epidermal cells. 总被引:14,自引:1,他引:13
In the epidermis of skin, a fine balance exists between proliferating progenitor cells and terminally differentiating cells. We examined the effects of TGF-beta s and retinoic acid (RA) on controlling this balance in normal and malignant human epidermal keratinocytes cultured under conditions where most morphological and biochemical features of epidermis in vivo are retained. Our results revealed marked and pleiotropic effects of both TGF-beta and RA on keratinocytes. In contrast to retinoids, TGF-beta s acted on mitotically active basal cells to retard cell proliferation. Although withdrawal from the cell cycle is a necessary prerequisite for commitment to terminal differentiation, TGF-beta s inhibited normal keratinization in suprabasal cells and promoted the type of differentiation commonly associated with wound-healing and epidermal hyperproliferation. The actions of TGF-beta s and RA on normal keratinization were synergistic, whereas those on abnormal differentiation associated with hyperproliferation were antagonistic. These observations underscore the notion that environmental changes can act separately on proliferating and differentiating cells within the population. Under the conditions used here, the action of TGF-beta s on human keratinocytes was dominant over RA, and TGF-beta s did not seem to be induced as a consequence of RA treatment. This finding is consistent with the fact that RA accelerated, rather than inhibited, proliferation in raft cultures. Collectively, our data suggest that the effects of both factors on epidermal growth and differentiation are multifaceted and the extent to which their action is coupled in keratinocytes may vary under different conditions and/or in different species. 相似文献
95.
96.
Inhibition of nitric oxide synthesis increases mortality in Sindbis virus encephalitis. 总被引:9,自引:5,他引:4
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Sindbis virus (SV) is an alphavirus that causes acute encephalomyelitis in mice. The outcome is determined by the strain of virus and by the age and genetic background of the host. The mortality rates after infection with NSV, a neurovirulent strain of SV, were as follows v: 81% (17 of 21) in BALB/cJ mice; 20% (4 of 20) in BALB/cByJ mice (P < 0.001); 100% in A/J, C57BL/6J, SJL, and DBA mice; and 79% (11 of 14) in immunodeficient scid/CB17 mice. Treatment with Nomega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthetase (NOS) inhibitor, increased mortality to 100% (P < 0.05) in NSV-infected BALB/cJ mice, to 95% (P < 0.001) in BALB/cByJ mice, and to 100% in scid/CB17 mice. BALB/cJ and BALB/cByJ mice had similar levels of inducible NOS mRNA in their brains, which were not affected by L-NAME or NSV infection. Brain NOS activity was similar in BALB/cJ and BALB/cByJ mice before and after infection and was markedly inhibited by L-NAME. NSV replication in the brains of BALB/cJ mice, BALB/cByJ mice, and mice treated with L-NAME was similar. Treatment of N18 neuroblastoma cells with NO donors S-nitroso-N-acetylpenicillamine or sodium nitroprusside in vitro before infection increased cell viability at 42 to 48 h compared with untreated NSV-infected N18 cells with little effect on virus replication. These data suggest that NO protects mice from fatal encephalitis by a mechanism that does not directly involve the immune response or inhibition of virus growth but rather may enhance survival of the infected neuron until the immune response can control virus replication. 相似文献
97.
98.
Dong-Uk Kim Seung-Kiel Park Kyung-Sook Chung Myung-Un Choi Hyang-Sook Yoo 《Molecular & general genetics : MGG》1996,252(1-2):20-32
ASchizosaccharomyces pombe homolog of mammalian genes encoding G protein subunits,gpb1
+, was cloned by the polymerase chain reaction using primer pairs that correspond to sequences conserved in several G genes of other species followed by screening of genomic and cDNA libraries. Thegpb1 gene encodes 317 amino acids that show 47% homology with human G
1 and G
2 and 40% homology withSaccharomyces cerevisiae G protein. Disruption of thegpb1 gene indicated that this gene is not required for vegetative cell growth. However,gpb1-disrupted haploid cells mated and sporulated faster than wild-type cells, both in sporulation (MEA) and in complex medium (YE): when examined 23 h after transfer to sporulation medium, 35% ofgpb1-disrupted haploid pairs had undergone conjugation and sporulation, whereas only 3–5% of wild-type haploid pairs had done so. Overexpression of thegpb1 gene suppressed this facilitated conjugation and sporulation phenotype ofgpb1-disrupted cells but did not cause any obvious effect in wild-type cells. Co-disruption of one of the twoS. pombe G-subunit genes,gpa2, in thegpb1-disrupted cells did not change the accelerated conjugation and sporulation phenotype of thegpb1
– cells. However, co-disruption of theras1 gene abolished thegpb1
– phenotype. These results suggest that Gpbl is a negative regulator of conjugation and sporulation that apparently works upstream of Ras1 function inS. pombe. The possible relationship of Gpbl to two previously identified, putative G proteins ofS. pombe is discussed.A preliminary report of this work first appeared in an abstract of the Genetic Society of America, 1993 Yeast Genetics and Molecular Biology Meeting, p. 92 and was presented at the American Association of Cancer special meeting on Cell Signalling and Cancer Treatment, 1993 相似文献
99.
Distinct tyrosine phosphorylation sites in ZAP-70 mediate activation and negative regulation of antigen receptor function. 总被引:9,自引:4,他引:5
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G Kong M Dalton J B Wardenburg D Straus T Kurosaki A C Chan 《Molecular and cellular biology》1996,16(9):5026-5035
Biochemical and genetic evidence has implicated two families of protein tyrosine kinases (PTKs), the Src- and Syk-PTKs, in T- and B-cell antigen receptor signaling. ZAP-70 is a member of the Syk-PTKs that associates with the T-cell antigen receptor and undergoes tyrosine phosphorylation following receptor activation. Three tyrosine residues, Tyr-292, -492, and -493, have been identified as sites of phosphorylation following T-cell antigen receptor engagement. Utilizing ZAP-70- and Syk-deficient lymphocytes (Syk-DT40 cells), we provide biochemical and functional evidence that heterologous trans-phosphorylation of Tyr-493 by a Src-PTK is required for antigen receptor-mediated activation of both the calcium and ras pathways. In contrast, cells expressing mutations at Tyr-292 or -492 demonstrate hyperactive T- and B-cell antigen receptor phenotypes. Thus, phosphorylation of ZAP-70 mediates both activation and inactivation of antigen receptor signaling. 相似文献
100.
Summary A heterologous gene from bloodsucking leech for anticoagulant, hirudin, has been expressed in the methylotrophic yeast Hansenula polymorpha. The addition of 1%(v/v) soybean oil to the medium as a stabilizer enhanced the expression of the hirudin gene in H. polymorpha with MOX promoter. The production of hirudin in the medium with soybean oil was 320mg/L in a 5L fermenter. 相似文献